Pack your cozzie, we’re going to the Arctic. It’s going to be hot and steamy. There will be palm trees and crocodiles.

This is the Paleocene-Eocene thermal maximum, or PETM, of 55 million years ago. For the past few million years, Earth has gradually been getting hotter and hotter and is now on the verge of a planetary heatwave the likes of which have rarely been seen.

Even before the mercury peaks, it’s pretty toasty. The poles are essentially ice-free, the deepest reaches of the oceans are 8 °C warmer than today, sea levels are roughly 70 metres higher and there are crocodile-like champsosaurs in the Arctic Ocean. The fact that they thrived so close to the North Pole means water temperatures must have been no less than 5 °C even in the permanent darkness of winter. Today’s average winter temperatures at the North Pole hover around -34 °C. You may also catch a glimpse of the hippopotamus-like Coryphodon in the warm swampy forests along the ocean shores.

Fast-forward a few million years and you will see freshwater turtles, which seems bizarre until you consider that the Arctic basin is almost entirely enclosed by land. River water streaming off the land is floating on top of the heavier saltwater, forming what may have been one of the biggest lakes the planet has ever seen. Great for swimming, too, as the water is a pleasant 23 °C.

The other end of the world would also have been experiencing swimsuit weather. “At the peak of the PETM you get …